Methods of controlling braking for a vehicle having a plurality of wheels fitted with tires and brakes are known, with the control method generating a braking set-point for each wheel in response to a braking order. The control method includes anti-lock protection, e.g. comprising the following steps for each wheel:                estimating the slip rate of the wheel as being equal to τ=1−Rω/v where R is the rolling radius of the wheel, ω the angular velocity of said wheel, and v the longitudinal speed of the aircraft; and        if the slip rate is greater than an optimum slip rate, reducing the braking setpoint for the wheel so that the slip rate returns to being less than the optimum slip rate, the optimum slip rate being that for which the tire fitted on the wheel co-operates with the runway to develop a maximum coefficient of friction.        
The braking setpoint may equally well be constituted by a hydraulic pressure applied to pistons when the brake is a hydraulic brake, on a force applied by the pushers of electromechanical actuators when the brake is an electric brake, or indeed a braking torque to be developed by brake in question.
That control method serves to limit wheel locking, thereby considerably improving braking performance and enabling the vehicle to be stopped over shorter distances.
In general, the optimum slip rate is predetermined, e.g. at a value of 8%. Nevertheless, it is known that the characteristics of friction between wheels and a runway are essentially variable and that the optimum slip rate can vary as a function of conditions encountered by the wheels on the ground (runway dry, wet, snow covered, icy, . . . ), such that the predetermined optimum slip rate cannot correspond to all of said conditions.
Estimation methods are known that serve to update certain characteristics of friction between the wheel and the runway. For example, document DE 10 2005 001 770 describes a method of regulating the slip rate in an anti-lock system, the method including the step of updating a parameterized grip model that is representative of a relationship between a coefficient of friction and a slip rate, and of deducing therefrom an updated optimum slip rate.
Similarly, document EP 1 372 049 describes how to determine an optimum slip rate, taking account of estimates or measurements, and how to regulate braking around that optimum slip rate.
Document US 2003/0154012 also discloses predictive anti-locking control which predicts a future slip rate on the basis of a non-parameterized grip model, in order to detect any tendency to locking and to modify accordingly the braking setpoint in order to avoid such locking.